Most of the conventional threaded members are made of metal materials. The metal materials have high activity so that the threaded members tend to oxidize and rust when exposed to the atmosphere. Under such circumstance, the threaded members are often jammed in a work piece and hard to unscrew. Accordingly, more strength and time are necessary for forcedly unscrewing the rusted threaded members. In some cases, it is necessary to break the rusted threaded members or the work piece for removing the threaded members. This is quite inconvenient.
A conventional way to prevent the threaded member from rusting is such that the periphery of a threaded member can be oiled. However, after a period of use, the oil is likely to dry out and lose its antirust capability.